1. Field of the Invention
The invention relates to a method of testing the susceptibility of electric circuits to electrostatic discharge (ESD). In particular it relates to the non-destructive testing of an IC device to determine the ESD performance.
2. Discussion of the Prior Art
The circuits of integrated circuit devices (IC""s) are invariably exposed to electrostatic discharge (ESD) through handling, typically during manufacture and installation of the component. It is therefore desirable to manufacture such circuits to have a certain resilience to ESD and to be able to make a determination as to the reliability of such IC devices. Various approaches have been adopted in the past to test the ESD performance of IC devices. These include such tests as the human body model (HBM), the machine model (MM), and the charged device model (CDM). All of these tests, as known in the art, are destructive in nature. Thus, the device is damaged to some extent by the testing process. These tests involve discharging a charge into the various pins, and subsequently testing the part, e.g., using automatic testing equipment (ATE).
The present invention seeks to address these problems.
According to the invention there is provided a non-destructive method of testing the ESD performance of an IC device, comprising probing the device with a laser beam, and monitoring the amount of light reflected from the device.
Typically, an infrared laser beam is used to probe the IC device, and preferably the energy of the laser beam corresponds substantially to the bandgap of the substrate of the device. In the case of silicon substrate integrated circuits, the energy of the laser preferably is about 1.1 eV.
The diffusions of the device are probed, and are typically probed through the back of the device. Typically, an I/O cell is probed to determine how much light is absorbed and how much light is reflected by the diffusion, and preferably, several samples are taken of each probed location, and the results averaged. A pulsed laser, also known as a mode-locked laser (ML) is used to probe the IC device. Typically, however, a continuous wave laser is used in addition to the mode-locked laser, to provide an image of the IC device in order to facilitate the positioning of the mode-locked laser beam.
Testing may be performed on the device in its final packaged state or prior to packaging, and even prior to completion of all of the layers of the device. For purposes of this application, the term device includes pre-packaged devices and devices that include only some of the layers of the final IC device.
The testing is typically performed with power supplied to the device, and the laser beam may be positioned manually by a user, or automatically, using image recognition technology.